Internal combustion engines typically include one or more pistons interconnected by connecting rods to a crankshaft. The pistons are typically disposed to reciprocate within bores formed in a crankcase. A typical piston includes a head portion, which at least partially defines a combustion chamber within each bore, and a skirt, which typically includes a pin opening and other support structures for connection to the connecting rod of the engine. In general, a piston is formed to have a generally cupped shape, with the piston head forming the base, and the skirt portion being connected to the base and surrounding an enclosed gallery of the piston. In typical applications, lubrication oil from the engine is provided within the gallery of the piston during operation to convectively cool and lubricate various portions of the piston.
A typical piston head also includes an outer cylindrical wall having one or more circumferentially continuous grooves formed therein. These grooves typically extend parallel to one another and are appropriately sized to accommodate sealing rings therewithin. These sealing rings create sliding seals between each piston and the crankcase bore it is operating within. Typically, the groove located closest to the skirt of the piston accommodates a scrapper ring, which is arranged to scrape oil clinging on the walls of the piston bore during a down-stroke of the piston. Oil that may remain wetting the walls of the bore following the down-stroke of the piston may enter the combustion chamber and combust during operation of the engine.
In general, the piston operates by reciprocating within a bore formed in a cylinder case of the engine, which creates a variable volume that can compress a fuel/air mixture provided therein. The combusting fuel/air mixture expands and pushes the piston to increase the variable volume, thus producing power. Fuel can be provided directly or indirectly within the variable volume, while air and exhaust gas is provided or removed from the variable volume through one or more intake and exhaust valves that selectively fluidly connect the variable volume with intake and exhaust collectors.
The materials used to construct the walls of the engine cylinders, the piston, the various valves associated with the variable volume, and other surrounding engine structures, are selected to withstand high temperatures and pressures that are present during engine operation. Various features of the piston are also shaped to promote the efficient burning of fuel within the piston, reliability of the various engine components associated with the engine cylinders, and other considerations. However, it is always desired to increase the reliability and service life of these and other engine components, as well as promote the efficient operation of the engine in terms of reducing fuel consumption and emissions and increasing power and efficiency.
One example of an engine piston having shaped features to promote efficient fuel burning can be seen in U.S. Pat. No. 7,942,126 (the '126 patent), which is directed to a “Method for Operating an Internal Combustion Engine and Internal Combustion Engine for such a Method.” The '126 patent describes a piston top having integrally formed therein a piston recess which merges into an essentially annular stepped space, and an injector forming injection jets directed toward the stepped space.
According to the '126 patent, the injection jets are deflected by the stepped space into a first part quantity of fuel, which is directed in an axial direction and a radial direction into the piston recess, and a second part quantity of fuel is deflected in the axial direction and the radial direction over the piston top and third part quantities of fuel are deflected into a circumferential direction so as to impinge one onto the other in the circumferential direction and to be deflected radially inwardly. As can be appreciated, for the engine of the '126 to operate as described, the start of injection and the injection duration must be precisely coordinated with one another and with the crank angle of the internal combustion engine. Such coordination, however, makes it difficult to operate the engine efficiently over a broad range of engine operating conditions and environmental factors such as temperature, which may affect engine operation.